1. Field of the Invention
This invention is concerned with damped flywheels for transmissions, especially for automotive vehicles. In particular, it is concerned with such damped flywheels comprising two coaxial parts, namely a primary part and a secondary part, which are mounted rotatably with respect to each other, and further comprising resilient means acting circumferentially between two annular components, each of which is associated with a respective one of the primary and secondary parts.
2. Description of the Prior Art
Damped flywheels of the above kind are described for example in U.S. Pat. No. 4,663,983 and French published patent document FR 2 571 461A.
For certain applications at least, it is desirable to obtain the lowest possible characteristic frequency for the flywheel, so that this frequency is as different as possible from that obtained when the engine of the vehicle is operating in reverse. This characteristic frequency depends mainly on the stiffness of the resilient means employed. It also depends on the clearance, commonly called dead centre clearance, which is usually provided in the vicinity of dead centre. There is no operation of resilient means during the angular displacement which takes place while this clearance is being taken up, and the equivalent stiffness of the assembly is thus reduced, and thus also the characteristic frequency.
In the above mentioned patent documents, the dead centre clearance occurs partly between one of the annular components concerned and partly between the resilient means. The relevant annular components consists in practice of a damper plate which is provided with arms arranged to act between the resilient means, the latter being jointly retained and engaged endwise by the other one of the annular components, which comprises two rings normally referred to as guide rings. A consequence of such an arrangement is that the dead centre clearance is detrimental to the space which is available for location of the resilient means, and this in turn limits their circumferential length.
It is also possible to reduce the stiffness of the resilient means by increasing their length, but this has the effect of reducing the dead centre clearance.
It has therefore not been possible to address the disadvantageous effects of one of these factors without producing a correspondingly detrimental effect on the other.